1. Field of the Invention
The present invention relates generally to record media and, more particularly, is directed to a record medium suitably applied, for example, to a magneto-optical disk, an optical disk and so on.
2. Description of the Prior Art
An an optical record medium, a magneto-optical disk, has been developed in which a tracking guide groove of spiral or concentric shape is pre-formed on a disk and this pre-formed guide groove or the land portion between adjacent guide grooves is utilized as a recording track, whereby data can be recorded in and reproduced from the recording track along the track direction using the magneto-optic effect. In such record medium, by optically detecting the guide groove, data is recorded and reproduced in a magneto-optic fashion under the application of a tracking servo.
Incidentally, in such record medium, if data such as an operating system, a fundamental dictionary or the like used only for reproduction are supplied in the form such that they are pre-recorded on the record medium, then it becomes very convenient not only for the maker to supply program software but also for the user to use such record medium. For this reason, a record medium such as a disk or card is proposed, in which an area from which data is read out only (hereinafter referred to as a ROM (read only memory) area) and an area in which data can be recorded (hereinafter referred to as a RAM (random access memory) area) are provided in a mixed fashion.
FIG. 1 shows an example of a magneto-optical disk provided as a record medium in which data for only reproduction is pre-recorded. In FIG. 1, reference numeral 1 depicts a magneto-optical disk, in which there are provided a so-called RAM area 1a in which a signal can be recorded and a so-called ROM area 1b from which a signal can be read out only. In that case, within the RAM area 1a, a pre-formed guide groove or a land portion between the guide grooves is employed as a recording track 1a', and data is recorded on the recording track 1a, in a magneto-optic fashion. Further, on the ROM area 1b, there is provided a track 1b' in which data for only reproduction is pre-recorded in the form of, for example, a pit train. While the RAM area 1a and the ROM area 1b are provided in the perfectly separated condition as shown in FIG. 1, it is frequently observed that the track 1a' of the RAM area 1a and the track 1b, of the ROM area 1b are provided in a mixed state.
Instead of the above-mentioned magneto-optical disk, a card type record medium is proposed, in which a RAM area and a ROM area are provided in a mixed state. FIG. 2 shows an example of such previously-proposed card type record medium.
As shown in FIG. 2, a magneto-optical card 20 is composed of a RAM area 21 and a ROM area 22, wherein a plurality of grooves are formed in the RAM area 21 at predetermined intervals and a plurality of pit trains are formed in the ROM area 22 at predetermined intervals.
However, in the record medium in which the RAM area and the ROM area are provided in the mixed state, different tracking servo must be applied to the RAM area in which data is recorded in the grooves by utilizing magneto-optic effect than to the ROM area in which data is recorded in the pit trains. For this reason, a continuous tracking servo cannot be applied to such record medium by a single tracking method, thus a recording and reproducing apparatus having a complicated-arrangement for the tracking function is required.
To solve the aforenoted problem, the assignee of the present application has previously proposed the following record medium (see U.S. Pat. application Ser. No. 568,963), in which data is recorded on the ROM area by means of the displacement of the groove in its width direction, grooves are provided both in the RAM area and the ROM area and the tracking servo can be effected in both RAM and ROM areas on the basis of the detection of the grooves.
If the grooves are provided on the RAM and ROM areas under the same condition, there is then the disadvantage that data cannot be reproduced satisfactorily in any one of the RAM and ROM areas. For example, if the groove is provided on the RAM area in width and at a pitch so that a signal can be excellently recorded in the RAM area using to the magneto-optic effect, then a crosstalk occurs in an adjacent track in the ROM area due to the displacement of the groove in the width direction, thus hindering a signal from being reproduced from the ROM area satisfactorily. If on the other hand the groove is formed in the ROM area in width and at a pitch such that a signal can be satisfactorily reproduced from the ROM area, the recording of a signal utilizing the magneto-optic effect cannot be effected sufficiently in the RAM area, which increases an error rate of a reproduced signal.